This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application PRINTED CIRCUIT BOARD CAPABLE OF PREVENTING ELECTRICAL SHORT DURING SOLDERING PROCESS filed with the Korean Industrial Property Office on Mar. 13, 1999 and there duly assigned Serial No. 8509/1999.
1. Field of the Invention
The present invention relates to a printed circuit board, more particularly the printed circuit board capable of preventing electrical short during a soldering process.
2. Related Art
In a process of mass production of an electronic assembly, the connection between components and a substrate is accomplished by a heat-follow method or wave soldering method. The wave soldering method is mainly applied to a substrate having hole type parts. A method for connecting the component and the substrate by wave soldering is disclosed in U.S. Pat. No. 5,000,691, to Olsson et al., entitled Pin Fastened To A Printed Circuit Board By Soldering, and U.S. Pat. No. 5,092,035, to McMichen et al., entitled Method Of Making Printed Circuit Board Assembly. In a process of connecting a hole part, the width of the conveyor of a general wave soldering machine and the temperature of a solder spot are controlled to be matched to the dimension of each printed circuit board. However adequately controlled conditions are during the soldering process of a substrate, though, unexpected problems, for example an open joint due to lack of solder or a bridge joint due to excess solder, may occur.
The problem of a short-circuit, or xe2x80x9cshortxe2x80x9d, on a printed circuit board during wave soldering occurs as follows. A printed board incorporating a semiconductor device, for example a connector, is preheated at a predetermined temperature to match a condition for soldering. Then the heated printed board is passed through a pot containing molten solder, called the solder pot, to be heated at a predetermined temperature. On the lower surface of the printed board, pins of the connector protrude downward through holes formed in the printed board. The protruding pins of the printed board are soldered by wave soldering during the passage through the solder pot. In this state, the printed board is carried by a conveyor at a constant speed. Protruding pins of the printed board are skimmed along the surface of the molten solder in the solder pot. Therefore, a first pin protruding from a first hole is soldered and gradually a second pin of a second hole is soldered.
During the soldering process, some amount of the solder is pushed and flows along the line passing through the first hole and the second hole on the lower surface of the printed board covered with solder mask. Explaining in more detail, the lower surface of the printed board is covered with a solder mask to prevent soldering on the surface, but the solder mask is taken off at the region of the hole of the printed board, therefore the region of the hole is the region capable of being soldered. As mentioned above, some amount of solder mounted on the lower surface is not soldered to the region covered with solder mask and is pushed to the opposite direction of the moving direction of the printed board in regular sequence. But, when the pushed solder reaches the second hole in front to the patterns, there is no further passage to flow. Therefore, some amount of solder not flowing backward remains at the holes in front of patterns, which causes problems. An excess amount of the solder of adjacent holes are connected with each other, which yields a short. Also, an excess amount of the solder remaining in the hole is connected with adjacent pattern lines, which yields a short. When a short occurs, it is necessary to eliminate the zone producing an electrical short on the printed board, therefore labor and time for eliminating the zone are added to the production cost, raising the production cost and lowering the production efficiency.
Examples of the contemporary art of printed circuit board structures and methods for preventing electrical shorts due to bridging during soldering are seen in the following U.S. Patents. U.S. Pat. No. 4,339,784, to Shearer, entitled Solder Draw Pad, describes a printed circuit board provided with an additional foil pad arranged in line with a row of leads, which reduces bridging between adjacent leads during wave soldering.
U.S. Pat. No. 4,835,345, to Haarde, entitled Printed Wiring Board Having Robber Pads For Excess Solder, describes a printed wiring board with a solder pad of a special configuration at the downstream end of a linear array of solder pads. The downstream solder pad has an extra solder pad, or xe2x80x9crobber padxe2x80x9d, connected to the downstream pad by a solder-wettable bridge. The xe2x80x9crobber padxe2x80x9d and bridge are made of a solder-wettable, clean metal surface such as a fluxed, tinned, copper surface, and apparently are generally made of the same material as the solder pad.
U.S. Pat. No. 5,242,100, to Weeks, entitled Plated-Through Interconnect Solder Thief, describes a plated-through hole solder thief for inhibiting solder bridges between adjacent leads. The plated-through holes are located in the proximity of the last solder pad in a row of solder pads. Applicability to hole-mounted integrated circuits is also described.
U.S. Pat. No. 5,243,143, to Throop et al., entitled Solder Snap Bar, discloses a printed circuit board in which a snap bar is provided on the conductor side of a printed circuit board for reducing defect, including bridging, during soldering. The xe2x80x9csnap barxe2x80x9d is a portion of the circuit board""s conductor side which attracts excess solder from the leads, but is spaced away from the solder pads. As illustrated, the snap bar is a rectangular bar on the trailing edge of the solder pads. The snap bar is described as a clean metal surface which is fluxed prior to the wave soldering, and the snap bar is apparently generally made of the same material and by the same procedure as the solder pads of the printed circuit board.
U.S. Pat. No. 5,604,333, to Kennish et al., entitled Process And Structure For A Solder Thief On Circuit Boards, describes a process for minimizing solder bridges during wave soldering. Solder thieves are placed adjacent to a last pad of a series of pads, where the solder thief is approximately the same width and twice the length of the pad. The solder thief touches the last pad, and may be an extension of the last pad. The solder thief is made as an additional pad, and is apparently made of the same material as the other pads.
However, these methods and apparatus require additional pattern structure on the printed circuit board. Moreover, solder bridging is not always eliminated by these methods.
Therefore, it is an object of the present invention to provide an improved printed circuit board for wave soldering.
A further object of the present invention is to provide a printed circuit board capable of preventing an electrical short due to solidification of excess solder at the special point on the bottom side of the printed circuit board during a wave soldering process.
A still further object of the present invention is to provide an improved method of wave soldering.
A yet further object of the invention is to provide a method which lowers the cost and the production time.
In order to attain the above objects, according to an aspect of the present invention, there is provided a printed circuit board containing pin-through holes, which includes components for mounting on the printed circuit board to be electrically connected with the printed circuit board, wherein each of the components includes a plurality of pins for inserting into the pin-through holes, patterns formed on the printed circuit board, wherein the patterns are located adjacent to a last one hole among the arranged pin-through holes, and at least one zone formed on at least one of the patterns, wherein a surface of the at least one zone is capable of being soldered, and wherein the at least one zone is formed on the same line passing through the plurality of pins and to absorb an excess amount of the solder at the last one hole, which prevents an electrical short due to the excess solidification of the solder at the last solder.
In the printed circuit board according to the invention, the at least one zone includes a region in which a solder mask covering surfaces of the patterns is stripped off. Here, the xe2x80x9cstripped offxe2x80x9d region may be stripped off after the solder mask is applied, or may be a region in which no solder mask is applied.
Furthermore, in the printed circuit board, the at least one zone is formed in turn on the patterns. Still further, in the printed circuit board, a size of the at least one zone is gradually reduced in proportion to the interval between the last hole and the at least one zone.
According to another aspect of this invention, there is provided a printed circuit board containing pin-through holes which includes components for mounting on the printed circuit board to be electrically connected with the printed circuit board, wherein each of the components includes a plurality of pins for inserting into the pin-through holes, and a dummy zone formed on the printed circuit board, wherein the dummy zone is located adjacent to a last one hole among the arranged pin-through holes, wherein a surface of the dummy zone is capable of being soldered, and wherein the dummy zone is formed on the same line passing through the plurality of pins and to absorb an excess amount of the solder at the last hole, which prevents an electrical short due to the excess solidification of the solder at the last solder.
In the printed circuit board according to the invention, the dummy zone includes a region in which a solder mask covering surfaces of the printed circuit board is stripped off. Furthermore, in the printed circuit board, the dummy zone is located at an opposite direction to a moving direction of the printed circuit board during a soldering process.
Still further, in the printed circuit board, the dummy zone includes a first portion spaced apart from the last hole and a second portion to connect the first portion with the last hole. Still further, in the printed circuit board, the width of the second portion is smaller than a radius of the last hole.
The present invention will be better understood from the following detailed description of the exemplary embodiment thereof taken in conjunction with the accompanying drawings, and its scope will be pointed out in the appended claims.